The Greenest House in the World… Eco-Sense Cob Home

The Greenest House in the World… Eco-Sense Cob Home

Ann and Gord built what is called the World’s Greenest Modern House in the world” from the greenest building program ever created. Their cob – “mud” home includes energy and water conservation, composting toilets, solar photovoltaics, solar thermal: domestic hot water and heating, rainwater harvesting, living roofs, earthen floors and counters, natural non-toxic – no or low VOC finishes and food gardens as well as honey bees.. all in an exceptionally beautiful yet really affordable home. Their motto is Less Life Stuff, More Life Style!

model of cob home

A model made of the home showing the living roof and solar panels

Ann and Gord met and were married within six months. A year later the couple bought 8 acres on Canada’s Vancouver Island, sharing the purchase with Ann’s parents. The couples then moved into trailers on the land. Ann and Gord shared theirs with Gord’s two children and a border collie.

They wanted to build a home that was as sustainable as the building code would allow but also wanted to push the current sustainable building policies and boundaries. The original intent was to build a straw bale home but the more they read about cob the more they liked it.

The site had been used as a garbage dump and was damaged. The couple planned to clean it up so it was better than new. Their goal was to build a multi-generational home that functioned in such a way that no line separated the dwelling from the rest of nature. They would share energy, resources and water and the eco system would be better off for it.

The home took 20 months from start to finish. The couple did most of the research and building themselves but hired professionals and individuals as needed.

The Building and Thermal Mass

The couple says that the lifespan of a conventional house is only around 35 years. Cob has an expected lifespan of about 500 years. Houses use a lot of valuable resources and energy and you are fighting nature all the way. We all win when a home is truly built to last.


Ann and Gord’s kitchen features recycled wood with an earthen counter insert. Note the DC powered, energy efficient chest fridge on the left.

The final home is a 2,150 square foot, five bedroom, two bathroom, two kitchen, cob building, that functions like a duplex but technically is not. The way their building inspector approached it is that they have a really big kitchen with a small hallway to separate the two halves. Ann and Gord and the two children live on one side of the home and Ann’s parents in the other.

The couples share a mud room entrance, freezer, washing machine, utilities as well as the phone line, but have semi-private living facilities. A little pass through window was built between the kitchens  and makes it easy for the sides to converse.

The cob walls are almost two feet thick and are a solid mass. Ann and Gord say that even though the cob may have a lower R value (R-1 per inch) it functions as a much higher one. Their walls perform like a R-24 wall and they have the research to prove it. The difference is that they have analyzed their home as a system, not just one component, unlike the existing building code.

Cob home living room

Ann and Gord’s comfortable living room has built-in Hydronic heated seating as well as heated earthen floors. The walls are finished with home made milk paints.

The roof is insulated with formaldehyde-free fiberglass and the floors have a R-12.5 rigid Styrofoam. The majority of the inside has an earthen floor – clay, sand and straw, the same materials as the house. This consists of three to four inches of cob with Hydronics for heating in the floors as well as built-in benches. This has been finished with several coats of boiled linseed. Linseed oil is an oxidizing oil that becomes very hard. 2 coats of a hard wax follows.

80% of wood in the house is recycled and the cupboards are Gord’s first attempt at carpentry. Wood with earthen counter inserts top these cupboards. Ann and Gord do courses on earthen floors and counters and have written a little booklet (english and french translation) on the method for their blog.

When you are doing plasters you need to have your fibres short. This can be done by running through a weed wacker or a chipper, but the couple does it by running it through a horse. Yes, they use horse manure. Ann says in the beginning she had gloves on and the thought of touching pooh was weird, but you hear about people using different manures all over the world, you get used to it and realize that it is a really useful material. She now exploits the merit of using this pre-chopped mixture.


A cob home is made out of clay, sand and straw, mainly dirt made into mud. The couple also added a locally mined pumice, giving additional insulation to the thermal mass.

You take moist clay – pottery moist, and add the straw and sand, then mix it together. The consistency should be like cookie or bread dough. To build, you stack the mixture a handful at a time and it gives you a heavy dense wall system. The walls are eyeballed as you build as you don’t use forms. If a wall seems out of kilter a hand saw is used to shave it into shape. Each wall is built up to about eight feet high. The walls are left to dry and once dry additional shaping can take place.

The couple says they got used to the process so in time it was quicker as they had less shaping to do.

Clay and Moisture

Work shop building

Ann and Gord do work shops on cob building and this attractive root cellar with a built-in bench is one of the results.

A bonus with Clay is its ability to control moisture. Dried clay holds a moisture content ranging between one and six percent. This ability to hold moisture has allowed currently occupied European cob buildings to last as long as 700 years.

A 14% or greater moisture content in a material is an opportunity for insects to move in, above 20% then funguses can live. With cob’s lower percentage neither insects not funguses can survive and the clay becomes inert, like stone. The walls resist humidity problems, mold or condensation.

The Foundation

The home has a concrete foundation and a fabric form was used. The couple says the fabric form is “an awesome material to use”. Using fabric gives you less waste, less wood for forms and it is easy to make curves, something that saves time and money.

The concrete the couple used is re-enforced and has a high fly ash content (45%) which reduces the carbon content of the material. Traditional concrete uses Portland cement which has a heavy ecological footprint and fly ash reduces the amount of Portland. For every ton of Portland Cement there is a ton of carbon emitted in that building process. If you can take some of that Portland out you can replace it with other by-products of the cementing process, whether it be fly ash, silica fume, volcanic ash or pulverized Baker clay baker bricks. It takes longer to cure but it lasts longer because it mineralizes different. See ECOsmart Concrete.

Pumice was also added to the concrete. This addition was thought to increase the R-value but unfortunately research showed it didn’t.


Ann and Gord’s home is one of the first load bearing legal cob residence in North America, a feat that really pushed their structural engineer. The couples live in an earthquake zone and say the area is overdue for “the big one” therefore the building needed to withstand a quakes force with little damage, if any. Traditionally cob can withstand minor movement as the straw in the mixture works like mini rebar, the couple wanted their home to be even stronger.

cob home truth window

The truth window shows the aircraft cable in the walls

They first poured the concrete foundation, adding aircraft cable loops sitting out of the edges every 2 feet. The cob walls are then built and when you get to the top you there’s a concrete bond beam that mirrors the foundation. The result is a reenforced concrete ring around the top of your cob. Then you come back and you sew it together by diagonal tension cables. It is engineered so that if the foundation moves in an earth quake the cables get tighter, pull down tight and suck the concrete cap onto the cob. This puts the cob under compression, a feat which cob likes, stopping any deformity.

The cob walls were reinforced using a geotextile, normally used in bank stabilization, running a horizontal strip every 2 feet. If a crack should happen it will stay in that 2 foot strip and not continue past this point. You might see a crack on the surface but it won’t compromise the structure.

Milk paints

The wall are finished with a homemade milk paint. Ann did several experiments and written a little booklet on the process. She also says the process is not a secret and there a various books on the subject.

She says that you can buy manufactured milk paints but is expensive, ships a long way and has a carbon foot print, so it is better to make it at home. She found it interesting that when she previously had paint cans they went into a little tox corner in a garage or workshop. Now when the couples does plasters or painting she lets these non-toxic plasters go hard and they stay in the plaster shed. When you want to use them you add water and they are ready to go.

Milk Paint Recipe Links

Martha Steward Milk Paint Recipe
Earth Pigment Non-toxic Pigments, Mica Powders and Mediums
E-How Milk Paint Techniques


cob home composting toilet

Ann and Gord’s composting toilet. Note: the box on the left side is filled with shavings used instead of water for flushing.

As you step into the bathroom you notice that once the door is shut a light comes on. The couple ran DC for all of their lighting and put a DC pin switch in. It also allows for a little fan.

Bathrooms on both sides uses a composting system based on the Joseph Jenkins Humanure Handbook. It operates without water and the resulting “deposits” are turned into a rich, odorless compost. The toilet has a cabinet with two – five gallon buckets inserted under the seat. Flushing is done by adding shavings to the bucket. Once the buckets are full – usually once a week – they are dumped into a compost area.

In order to satisfy permit conditions the couple had to install a conventional toilet first. They flushed it once and then were able to take it out.

The bathroom also features a fan that has been positioned low so as to exhaust air and vapor but avoids sucking the warmest air out of the room. They say “having a high fan rather than a lower one is just the way it has always been done and no one questions this.” Their method just makes better sense.

Earthen counters as well as recycled sinks and doors are featured as well as low flow fixtures. Gord created the cabinets on his side, Ann’s dad created his bathroom’s cabinets.

Showers on both sides are Tadelakt. Basically it is a lime plaster that is burnished with a smooth rock and then finished with an olive oil soap. Gord says it is not really hard work but it is tedious, taking about 4 days for each shower.

Net Zero Electricity

The couples electricity comes from a 2 kW grid tied solar array. They are net zero and sell the excess back to their utility.

Ann and Gord use renewable sources but really believe that the best way to conserve energy and electricity is through the lifestyle choices. It is a different relationship with energy and comes from realizing that energy comes at a big cost to our planet, people, communities and other living things. They are not hard done by and live as well as other families, they just realize that electricity is a gift and use it with respect to their environment.

The house uses 90% less electricity and water per person than the average household. They conserve electricity in two ways. The first is through lifestyle choices – simply choosing to have less stuff, meaning no dryer, dishwasher, microwave or toaster. They also use a laptop rather than a plugged in computer.

The other way is through efficiency. They use LED lighting throughout the house, path lighting so you don’t light up a room when you are not in it, corded rather than cordless phones, a DC powered Sundanzer chest fridge rather than a bigger upright fridge. Pumps, fridges and other systems in the house use DC power as efficiency is reduced when you convert from one power form to another. The laptop, TV, vacuum cleaner and blender run AC power. The home mechanical systems are extremely efficient as well.

When it comes to a cloths dryer they don’t want or even need one because of the way the home functions with moisture. You wash your cloths and if it’s winter time and even has been raining for weeks, everyone has a cloths rack in their room or can use the one in the mechanical room, you hang your cloths up and twelve hours later they are dry.

Solar Thermal Combination System

Ann and Gord’s solar thermal system uses 60 evacuated tubes to heat water that warms their earthen floors, as well as provides them with domestic hot water. Heat from the tubes runs the sun heated water through inner core coils on a 120 gallon storage tank.

The system is designed so that if the floors don’t require heat but the boiler’s running, the heat will go through the upper coil and heat the tank up. Water goes both ways – they can pull heat out or put heat back in with a couple of check valves. Normally with a hydronic system you have a circulation pump and manifolds that are controlled by electronic zone control valves turned on and off by way of a thermostat. The couple got rid of the main pump and valves to eliminate phantom loads. If there is no heat required there is no draw.

Each thermostat runs a little solar circulating pump so when a thermostat calls for heat, a pump comes on, the valve opens, hot water runs through that zone. In the coldest day of the year, with the system running at full tilt, they use about 360 watts of power to control the whole system. This is a very small amount and is similar to leaving a 100 watt bulb on for 3.5 hours.

Winters in the area are mostly cloudy so you need to have some way of heating water without the solar thermal.  An upper coil in the storage tank is used for heat takeoff (at least in the winter), pulling heat off the coil to run it through the floors. If there is not enough heat in the tank they turn on the highly efficient wood gasification system. The system burns at about 1880 to 2000 degrees Fahrenheit, with an exit temperature in the flu of 160 degrees. The rest of the heat is then trapped into the water jacket tied into the water storage system (hydraulic) that runs through the floors of the home. See figure 31 and 32 Eco-Sense Science Report.

Living Roof

The couple wanted to do a living roof but found buying one too expensive, they didn’t like the amount of plastic they contained and they wanted to be able to install it themselves, so they came up with their own design.

Ann and Gord's living roof model showing the materials and the order they are installed.

Ann and Gord’s living roof model showing the materials and the order they are installed.

The design starts with a waterproof membrane. They use a Firestone APM membrane, basically it is like a really thick pond liner, but actually a roofing membrane. If you want your water to be potable you have to be aware of the materials you use. The one the couple ordered has no fire retardants in it.

Then there is a really thick polyethylene non-woven geo-textile, the same as the material used in highways and dams as well as landscape stabilization. This is called Armtech 400 and acts as a cushion and puncture resistant layer. It helps for root protection and acts as a drainage layer.

On top of the Armtech they have perlite, which you can get from the horticulture stores.

A thin filter cloth follows, bought from a plumbing supply store. That is your drainage layer. So as water comes down it, you have the ability to shear the water off underneath the living layer without losing your dirt.

You need to have a material down that your roots can actually attach to so they don’t blow out in the wind. You can use straw but the couple used coconut husk matting. Again you can buy it from the same people that sell the geo-textile material as it is used in landscaping and is a landscape fabric. The material goes on and will rot in a period of 5 or 6 years. It then becomes compost.

Then on top of that the couple uses a combination of pumice, leaf mulch and a bit of soil and that makes the growing media.

Then the roof is planted with native plants.

The couple says that a more intensive roof can have a thicker growing medium but you would need more layers of materials and you have to make sure your roof is engineered for the additional weight.

Benefits of a living roof start with its

  • It has water filtration properties. Pine needles don’t get through.
  • It works as habitat replacement.
  • It makes it very quiet inside the home.
  • It is fire resistant. If fire were to land inside you get a big poof from the grasses but there is nothing else to burn.
  • PV panels produce more efficiently because they stay cooler during the higher season.
  •  It is very beautiful.

The living roof works as mini water shed. When you think about rainwater collection you have to account for first flush diverting, taking care of pollen, pine needles, bird pooh and the living roof looks after that. The amount of filtration they have to do before storage is decreased and the water comes out clean, like a creek or a water shed.

A 10,000 gallon (37,854 litres) tank stores their rainwater and is further used for irrigation of the food gardens.

Grey Water/Composting

Four grey water systems water the many fruit trees and gardens surrounding the home. One is plumbed into the house so if the well were to go bad they can add a couple of filters, a UV sterilizer, and have potable water.

Gardens in cob home

Ann and Gord grow their own vegetables and have a healthy garden fed by the grey water systems

The grey water that comes from the kitchen sink goes into a bin and then into a worm filter. The worms eat the bits of food acting like a surge tank or grease trap and turns it into worm casting, the best compost money can buy. They use that in the gardens. The water then goes to the very bottom of the hill to water trees. Another grey water system drains from the laundry room and looks after the plum trees and raspberry bushes.

A further system feeds from an elbow off the bottom of the kitchen sink. You take the elbow off of one of your sinks and you put a sanitary Y in it with a knife valve or a day valve. A bucket goes underneath. When you open it up, the water goes into the bucket, you close it and the water can go back to the grey water system. The couple says it is really good when you are washing your potatoes or similar and is one of those $17 fixes you can put in your house that can be used to water plants in your house or balcony.  It is important to remember to close the valve if you don’t want to mop up the floor.

Human Manure/Compost

The waste from the bathroom – human manure, goes to a compost pile. Even though the couple adds to the heap regularly you don’t smell much except for hot straw. The process is called thermophylic composing. When you have the right balance of carbon (feces) and nitrogen (urine) – as well as wood shavings and kitchen scraps, you have the perfect environment for thermophylic bacteria to thrive. When they thrive they produce a lot of heat and when they produce a lot of heat they essentially pasteurize the compost.

cob home compost heat sensor

A gauge from the thermophylic compost pile that uses heat and then time for composting.

The couples adds to a pile for a year, let it go through its heating cycle and at the end of the year it sits dormant for another, letting time do its thing. After two years of composting the first thermophylic, and the second metaphysically, they send samples to a lab for a bacterial analysis, coming back completely food safe.

Other Buildings

  • Work Shop. The couples first engineered out building.
  • Earth Sheltered Greenhouse. Featuring a built-in bench and bread oven.
  • Off-Grid Chicken coup. A mini version of the house with natural plaster, solar panels with used car batteries, living roof, recycled materials, fully insulated.
  • Cob Root Cellar. Also features a bench. Created during a work shop held by the couple (photo below).

No Waste Building

The couple showed us a special apple tree planted where they manufactured the house. This means the walls, floors, paints, insulation, plasters and everything was processed as well as the waste. Normally when a home is being built you would have a dumpster and take the waste to the landfill. The couple uses the tree as a front yard litmus test to prove that it is non toxic that’s symbolic of traditional building versus low impact building. They proudly boast that they produced almost no garbage in the build nor was waste was shipped into someone elses back yard or for future generations. The impacts are in their front yard because they can eat the fruits of their labours.


Finally, what the couple has done is to build an affordable home. The average cost to build a home in their area is $277 per square foot. A low-end house is $160 sq ft. Their home came in at $148 sq ft. including $80,000 worth of sustainable energy systems. On top of that with those systems in place they don’t have monthly utility bills. If they were to take the systems out and put in conventional heating and electrical the cost would be down to around $110 sq ft.

Living Building Challenge

The Living Building Challenge is an international green building rating system, that is the brainchild of Jason McLennan, CEO of Cascadia Green Building Council, and International Living Building Institute.  This international green rating system strives to ensure the build environment is regenerative to the ecosystems that we share and live within. Ann and Gord’s home achieved Petal Certification in October 2010, and as of Sept 2011. Jason called their home “The Greenest Modern House in the World as it was rated by the greenest rating system ever created. The couple achieved 4 four of the 6 petals (12 of the 16 prerequisites).

Cascadia report: Affordable Sustainable Homes:  Eco-Sense and the future of Green Building.

The couple says that they really try to reduce their carbon footprint with every project. For the living building challenge they had to do a full carbon analysis on the house. The highest was the concrete foundation and the membrane on the living roof but when you take into account everything else on this piece of land plus all the habitat regeneration – this was a damaged site and the eco system is now much healthier – they actually built carbon neutral.

Education and consulting

First change the dialogue, get people interested. Ann and Gord make their living with sustainable consulting and tours. One of the goals is to spend a third of the time working, a third volunteering for the community and a third doing their own thing. They have recently gotten to that point and spend much of their time educating groups and individuals as well as building cob homes for others. Really they are teaching people how to work with nature, not against it.

There are several links to their site within this post but you can also keep in touch with them through their blog:


  1. It is an interesting site. I really like the Jot Pad. Several of the people in this site have built their homes themselves. This includes Eco-Sense as well as the Northern California Straw Bale home and the Tantalus Resort Micro-Hydro Powered Off-Grid Retreat.

    Good luck with your build. It is an exciting time.

    Cheers, Terry

  2. Great site Terry. You may or may not have seen introduced by Kevin McCloud of Channel 4’s Grand Designs in the UK. Resources for planning the build of one’s life is at an exciting level. Time to doodle & plan in readiness for when the opportunity arrives…when I’ve no idea…soon I hope!

  3. The eco-sense cob home looks great when you see it in person. It just looks a bit different from most homes in the pictures. The building method is very very old and buildings can last hundred of years.

    I enjoyed talking to the couple who built the home and they are truly enspiring.

    You should also visit the post on the Earthships. Yes these are very very different but if you take the principles into account – not necessarily the building style – you have a home that works well in any climate and is very easy on the earth. See the post here: Earthship: A most Radically Sustainable Home.
    I am glad that you found the site. I built it because I love the idea of building better, more sustainable homes and although I have several eco elements in my personal home, I wish to build and live in an off grid home some time in my future.


  4. Superb. I came online to research hydro electric power. 3 articles later I’m at the world’s foremost modern eco build. Not aestheticly pleasing to my eye but certainly, Food for thought, Food for living, the components that make this way of life a necessity!


  1. […] Your ECO Friend – detailed blog post from a couple touring North America to write a book on Green architecture.  They did a very good job on the article and photos. […]

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